lymph is not actively pumped by the heart, but is pulled into the lymphatic capillaries by a pressure gradient (capillary action) and is forced through the vessels by similar mechanisms that help venous blood return to the heart: the contraction of skeletal muscles during body movements and the pressure gradients created by breathing.

simple squamous epithelium called the endothelium

venules and veins withstand a much lower pressure from the blood that flows through them

The skull, attached to the top of the vertebral column, is balanced, moved, and rotated by muscles located in the neck

origin of a muscle does not move

axial (muscles of the trunk and head) and appendicular (muscles of the arms and legs) categories.